In addition to the wild speculation by conspiracy theorists, experts and media types are floating a range of ideas as to what might have happened to Malaysia Airlines Flight 370, its 12 crew members, and the 227 passengers on board.

Without finding the plane or solid evidence of its whereabouts, there’s no telling exactly what caused the jetliner to vanish. So until that happens, here are the theories we’re working with:

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1. Pilot Suicide

Many of the theories being floated involve what officials are calling “human intervention.” Tragically, pilot suicide is one of them. It wouldn’t be the first time it has happened, either.

The Associated Press said two previous plane crashes were most likely caused by pilot suicide. A 1997 Silk Air crash on a flight from Singapore to Jakarta and a 1999 Egypt Air flight are both suspected to be caused by pilot suicide. The AP report cited Mike Glynn, a member of the Australian and International Pilots Association, as saying he believes that is the most likely cause.

Despite Glynn’s belief, officials don’t think the theory has much strength. More from the AP:

At this point, there is no evidence of any wrongdoing on the part of the two pilots, though Malaysian police have said they are looking at their psychological background, their family life and connections.

Zaharie Ahmad Shah, 53, and Fariq Abdul Hamid, 27, have both been described as respectable, community-minded men.

2. Pilot Sabotage

With the pilots’ backgrounds already under investigation, officials are also considering pilot sabotage.

Recent developments have led investigators to believe that an experienced pilot deliberately changed the course of the flight. Reuters reported that the plane diverted to a route that is well-known among navigators. From Reuters:

Two sources told Reuters that military radar data showed an unidentified aircraft that investigators suspect was Malaysia Airlines Flight MH370 following a commonly used navigational route toward the Middle East and Europe when it was last spotted early on March 8, northwest of Malaysia.

That course - headed into the Andaman Sea and towards the Bay of Bengal in the Indian Ocean - could only have been set deliberately, either by flying the Boeing 777-200ER jet manually or by programming the auto-pilot.

According to the Daily Mail, there were also deliberate efforts made to shut off the plane’s data system and transponder. The two were reportedly shut off at different times, seemingly ruling out the possibility of a crash. From the Daily Mail:

US officials believe that two communications systems aboard Malaysian Airlines flight 370 were shut down separately, 14 minutes apart - which indicates the plane did not come down because of a sudden catastrophic failure.

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That has led the US investigating team to become ?convinced there was manual intervention? which in turn means it was not an accident or massive malfunction that caused the plane to cease to be airborne.

Some officials have said that making those changes proves an experienced pilot was at the helm. As a result, they’re taking this theory very seriously.

3. Hijacking by Pirates or Terrorists

There is also the possibility that the pilots were not the only ones on the plane with flight experience.

The New York Times reported that the plane flew erratically and that its altitude drastically fluctuated. Officials said those details could mean any number of things, including that the person at the controls had some flight experience. Unfortunately, that means investigators cannot rule out trained pirates or terrorists.

ABC News reported that CIA Director John Brennan said the agency is still considering terrorism a possibility. He even went so far as to say that there are already unconfirmed claims of responsibility for the plane’s disappearance. From ABC News:

?I think there?s a lot of speculation right now,? Dir. John Brennan told the Council on Foreign Relations. ?[There have been] some claims of responsibility that have not been confirmed or corroborated at all. We are looking at it very carefully. We, the CIA, are working with FBI and TSA and others. Our Malaysian counterparts are doing everything they can to try to put together the pieces here. But clearly this is still a mystery, which is very disturbing.?

When asked whether he had ruled out terrorism as a factor, Brennan responded, ?No, I wouldn?t rule it out. Not at all.?

While different groups are being investigated, officials have not said that there is evidence tying the incident to any pirates or terrorist organizations in particular.

Because evidence suggests a knowledgeable pilot was controlling the plane, the above three theories are considered to be the strongest. However, officials have not ruled out any of the following possibilities.

4. Pilot Error

Pilot error is one of the weaker theories being considered because both pilots were relatively experienced. Zaharie Ahmad Shah, 53, had over 18,000 hours of flight experience and Fariq Abdul Hamid, 27, had nearly 3,000 hours.

While experts have agreed that is a good deal of experience, the pilots’ character has not gone unquestioned. In particular, an incident where Hamid entertained two young women in the cockpit of a 2011 flight has several officials wondering whether he could have made a mistake.

CNN noted that the weather conditions were reported to be good for the missing flight as it made its way from Kuala Lampur to Beijing. As a result, most officials don’t consider the weather to be a factor.

But some media outlets have drawn comparisons between the missing Malaysia Airlines flight and other planes that have had trouble with sudden or unexpected weather in the past.

NBC News said that a 1947 flight that vanished over the Andes Mountains was originally blamed on the pilot’s negligence, but was eventually ruled to be caused by severe weather.

And in a blog about the retired names of tragic flights, NPR mentioned the crash of Delta Flight 191 in 1985. The flight took off from Texas and the weather was sunny and hot, but the plane crashed after the appearance of a sudden microburst. The weather pattern brought strong winds and eventually the plane went down, killing more than 130 people.

7. Mechanical Failure

Investigators haven’t ruled out the possibility of mechanical failure, either.

The Telegraph said that in Marang, a town on Malaysia’s eastern shores, villagers told police the they heard a loud noise early Saturday morning, about the same time the missing plane lost communication with air traffic controllers. The report said one man even described the noise as sounding like the fan of a jet engine.

Officials have said that the most recent evidence seems to the suggest that the plane continued to fly after losing contact, but the Telegraph noted that some investigators have not completely ruled out mechanical failure.

8. Catastrophic Failure

A catastrophic failure was what many officials expected early in the investigation. The search for the missing plane initially focused on looking for wreckage, including two long oil slicks spotted in the ocean off Malaysia’s coast and Chinese satellite images of what was originally thought to be debris.

Officials determined that neither of those findings were related to the missing Malaysia flight, and have changed course to focus on possibilities that do not include a catastrophic failure.

9. Decompression

Some experts are considering the possibility that the plane’s cabin suddenly decompressed but was able to continue flying.

A CBS News report said that a decompressed chamber at high altitudes could leave everyone on board unconscious and unable to communicate with air traffic controllers.

However, the recent evidence suggesting a skilled pilot was controlling the plane contradicts this notion.